The subject matter disclosed herein generally relates to rotors for aircraft use and, more specifically, in-process static balancing of main rotor blades of the aircraft.
For a typical rotor blade of a rotary-wing aircraft, the blade must meet requirements for balance so that excessive vibration and stress levels of the blade do not result when it is used in the aircraft. The blade balancing also ensures that all main or tail rotor blades used on the aircraft have identical responses. In-process static-balance characteristics of the blade have a direct influence upon dynamic (i.e., spanwise and pitch-moment) balance of the blade and whether such dynamic balance falls inside or outside allowable limits.
More specifically, the blade is formed from several components, including a spar with counterweights, a trailing-edge pocket assembly having at least one skin (such as upper and lower skins with a core therebetween), and a leading-edge assembly having a leading-edge sheath and other structures. These components are typically secured to each other by a structural film-adhesive bond and/or other fastener.
Manufacture and assembly of the components introduce some variation in weight (i.e., mass), weight distribution (i.e., center of gravity), stiffness, and shape into the blade. The weight and spanwise moments of the blade are measured via a static mass-balance procedure during manufacture of the blade to compensate for the variation in the weight and weigh distribution of the components. The procedure often includes a whirl stand in which the blade is rotated with a master rotor blade having a selected weight and weight distribution. The response of the blade is observed and compared to that of the master blade, and any variation between the response/motions is indicative of variation in the weight or weight distribution of the blade compared to the weight or weight distribution of the master blade. Such variation is corrected in the blade by removing material or molded counterweights from the blade up to certain acceptable or feasible limits. The limits constrain how severe an out-of-balance condition of the blade can be corrected, resulting in potential scrapping of the costly blade.